The Duke is here!
The Iron Duke is our interpretation of the hot-rodded
British tone, with MI Amplification's
unmistakable marriage of flexibility and
simplicity in one package.
The class A/B power amplifier is built around a
pair of EL34s, and delivers 50W of clean output
power, with a switchable low power mode limiting
the Iron Duke's output power to 25W. This range
of output power is perfect for hitting the Iron
Duke's sweet-spot in a typical gigging scenario.
The '4 channel' preamp (in fact, 2 independent
channels with a foot-switchable gain boost) can
produce the whole suite of British inspired
tones, from clean to scream. But unlike the
standard British designs (and their various
derivates), the Iron Duke can be tuned to work
with virtually any guitar and pickup, thanks to
its bright and attack switches. Added to this
already amazingly flexible design, each of the 4
"channels" can be further hot-rodded with the
independent 'mod' switches, for a total of 8
different preamp voicings.
Finally, we've included a series insert FX loop,
and our unique negative feedback controls,
featuring not only presence and depth controls,
but also an industry first 3 position 'depth
frequency' switch for tuning the active
frequencies of the depth control.
Introduction and Philosophy
The Iron Duke is an amplifier we are truly proud
of. I must confess that as a 'design brief', I
thought the Duke was going to be a straight
forward affair, but boy was I wrong! You see,
there's a difference between doing something
adequately, and doing it well. It took us
nearly 18 months to arrive at a design that
ticked all the boxes.
So what's the philosophy behind the Iron Duke?
Well, there were a few things we wanted to
achieve with the Duke:
-
- Modern flexibility with a vintage vibe,
even with 'high gain' settings
-
- A gigging workhorse: simple to use in the
heat of battle and solid enough to work
under the most trying conditions
-
- A modern channel switcher, but with enough
depth of character to be used old school,...
one sound with the drive controlled by the
guitar volume.
-
- A clean sound which is both beautiful as
a standalone clean, and as a platform for
overdrive pedals.
-
- An overdrive sound which is fat, rich and
complex, but which also cleans up
beautifully
-
- In contrast to the standard interpretation
of the British sound, we wanted the Iron
Duke to have the ability to work with
any guitar without sounding shrill
and harsh, yet still retain the British
flavour. The 'standard' interpretation of
the British sound may sound good with
particular guitars and pickups (humbuckers),
but will often sound thin and shrill with
other guitars. This was something we
absolutely DIDN'T want.
-
- Global controls for matching the overall
character of the amplifier to a particular
guitar/speaker and player.
We feel very strongly that the Iron Duke has
achieved all of these things. Below is a
detailed description of each aspect of the
amplifier.
Preamp
There are two ways to think of the Iron Duke's
preamp, either as 2 independent channels with a
foot-switchable boost, or as 4 'channels', each
pair of channels sharing the EQ and gain
controls, but with independent volume controls.
For the sake of clarity we will use the latter
convention.
Unboosted Clean:
The green 'channel' has a feel which is inspired
by the class A British amps, as opposed to their
bigger brothers. The low end is tight and
controlled in order to mimic the feel of a combo
clean. The mids are full and the high end is
rich and detailed. Add to this the three
position bright switch, and you can go from
fatter rounded tones, to shimmery cleans. Our
power supply design helps keep the cleans
'forgiving' regardless of how hard you pick.
With the gain set 12 O'clock, humbuckers will
break up slightly, and with the gain dimed,
you're in vintage crunch territory.
Engaging the 'mod' switch for the clean channel
will extend the low frequency response of the
preamp, and fill out the sound, for more clean
density, or as the perfect 'full range' platform
for pedals.
Boosted Clean:
The blue 'channel' tips its hat to the
traditional bright channel of vintage British
amps, but with a more rounded top end. Despite
the shared EQ, the tone stack in this mode is
reconfigured to accentuate a fat midrange. This
"channel" is all about vintage crunch. Engaging
the mod for the boosted clean (B.Mod) tightens
up this channel and introduces extra clipping,
creating a formidable rhythm sound with a more
modern leaning.
Unboosted Overdrive:
The orange 'channel' is the hidden gem of the
Iron Duke. With the gain set to 9 O'clock it
will do a beautiful clean which rivals even the
green channel. At 12 O'clock, you're crunching
nicely, and with the gain dimed, the tone is fat
and creamy. With the attack switch, you can
match the top end response of the preamp to your
guitar, or add more bite. Due the finely tuned
'balance' of this channel, it also cleans up
beautifully, making this channel a wonderful
candidate for a set-and-forget old school tone.
The Mod switch introduces more clipping and
tightens up the channel to create a searing
modern gain sound.
Boosted Overdrive: The red
'channel' takes off where the orange left off.
The midrange is beefed up, creating a complex
swirl of harmonics, and ensuring that despite
the gain, this channel remains, rich and
organic. Of course, engaging the "B.Mod" switch
introduces extra clipping, and tightness,
pushing this channel to the edge of 'metal'
territory.
Of special note about this preamp design is its
ability to work with pedals, even on the
overdrive channel. The careful design preamp
design means that the resulting tone is the
perfect fusion of the character of your
favourite overdrive pedal with the natural
clipping of the Iron Duke's preamp.
Power Amp
As mentioned previously, the Iron Duke's power
amplifier utilised a pair of EL34's operating in
class A/B to produce an output power of 50W
clean. A design decision was made early on to
keep the operating voltage of the EL34's 'low'
so that they could be pushed without any
problems. This is in stark contrast to the
'standard' channel switching philosophy of
maximising output power by running the power
tubes at very high voltages. The usual thinking
is that in a channel switching amp, the
distortion will be generated exclusively in the
preamp, and the power amp will never be pushed.
However with the Iron Duke, we wanted to take an
old-school approach so that the power amplifier
could regain its rightful place as a legitimate
'player' in the tone game, while still
maintaining modern flexibility. In fact, we feel
the sweet spot for the Iron Duke is at the point
where the power amp is starting to clip.
This brings us to the second point about the
output power. With 50W output power, the Iron
Duke will hit that sweet spot in a typical live
scenario. For quieter gigs, the amp can be
switched down to low power to hit the same spot,
but at a reduced SPL. Does this mean it can't be
used in a quiet 'practise' setting? Of course
not! The Iron Duke will still sound wonderful at
low volumes, but as with any great tube amp,
will sound spectacular when things get cooking.
Finally, we should make mention of the presence
and depth controls. These control the high end
and low end response of the power amplifier.
However, one feature which the Iron Duke has
which is unique is the ability to tune the
frequency range of the depth control using the
'depth range' switch. The 'standard' design for
low frequency feedback is to have the depth
control affect frequencies around 100Hz and
lower. This is a good setting for adding a low
end 'modern' fullness to the sound. However, for
the types of tones we were envisioning, we
wanted to the Iron Duke to always retain a full
low-mid sound. By setting the depth range switch
to 300Hz, the depth control not only reinforces
the low frequencies, but also extends up to the
main 'body' of the guitar sound, ensuring that
the tone doesn't sound 'woofy' when the depth is
increased. The last setting of 1KHz increases a
very wide range of frequencies, adding a wide
range of flavours across its sweep.
Quality
The Iron Duke is built to the same exacting
standards that we build our other award-winning
amplifiers. To name just a few things:
-
- Our custom made transformers are rated at
3 times the output power of the amp and run
cool even at full power
-
- Our PCBs are 2.4mm double sided, through
hole, thick plated. We went through a dozen
iterations until we found a layout which
ensured the perfect tone.
-
- Over-spec'd mixture carbon film and metal
film resistors for tone and reliability
-
- the highest grade signal caps (e.g. WIMA
and silver mica caps), chosen after a very
long process of evaluation.
-
- full sized, long life, 24mm
potentiometers.
-
- Even the wire was carefully chosen! We
ended up using a mix of 3 different types of
signal wire because of their various effects
on tone!
All these reasons, and more allow us to
confidently offer a limited lifetime warranty on
the Iron Duke.
